Keto-enol substance in urine, matutinal or preoperative, was determined and traced for three weeks after operation, on various surgical cases of the abdomen. Results obtained were as follows. 1) Levels of KES in matutinal or preoperative urine were generally higher than normal, especially in case of acute inflammatory disease, and the rate of increase was proportionated to extent and severity of the inflammation. Upon non-inflammatory diseases, KES was noticeably increased in the late stage of stomach cancer, successively cholelithiasis, stomach cancer resected, gastroduodenal ulcer in order. In the cases with uncomplicating peptic ulcer the level was markedly low, but in the cases with complication of bleeding or stenosis slightly increased. 2) In the postoperative course, urinary KES was markedly increased within one to three days after operatron and later decreased until normal on the seventh day. In the non-inflammatory cases, KES was further decreased and returned to normal after three weeks. In the cases of stomach cancer and peptic ulcer with complication of bleeding or stenosis, on the other hand, KES was not become normal even after three weeks of operation. In the cases of stomach cancer simply laparotomized, KES was not recovered to preoperative level even after three weeks of operation. In the cases with acute inflammation the grade and duration of high leveled KES were marked with severity of inflammation, and later decrease in KES was also retarded, not becoming normal level even after three weeks of operation. In acute simple appendicitis, though, the level became normal within seven days after operation. 3) In the cases with postoperative complications urinary KES was increased, and showed retarded decreasing rate. 4) From the results obtained above, it was concluded that determination of urinary KES before and after operation was valuable for judging the course of postoperative recovery and the prognosis.